The disclosed invention relates to the field of the optical storage of analog or digital data and, in particular, to high density storage of analog or digital information on an optical recording disk having separate optical paths for read, write and coarse seek beams.
It is well known in the art to use a modulated and focused radiation beam, usually a laser, to record both digital and analog information on a recording surface. See e.g., U.S. Pat. No. 3,314,073, issued to Becker on Apr. 11, 1967. For example, there have been a number of different means taught for providing proper focus of the incident read beam on the disk surface, including focusing systems wherein light is diffracted by the tracks on the disk surface and, the diffracted beams then focused on independent photo-sensitive elements.
While phase diffracted reflected beams have been used to detect focus error, astigmatic focus systems have generally been the system most favored to provide focus information. To accomplish this, a cylindrical lens is used to astigmatize the beam reflected from (or transmitted through) the optical recording media. The astigmatized beam thereafter provides a spot having two focal points, which are detected by a quad detector system. With an astigmatic focus system, the device is in focus when the circle of least confusion is properly focused on the detectors. The quad detector, in response to the pattern focused thereon, generates control signals. For example, see e.g., U.S. Pat. No. 4,290,132, issued Sept. 15, 1981, to Kotaka; U.S. Pat. No. 4,059,841, issued to Bricot et al.; and U.S. Pat. No. 3,962,721, issued June 8, 1976, to deHaan.
Likewise, tracking of the device beams over the disk surface has generally followed well known techniques. In random access devices using disk shaped carriers, it has generally been necessary to provide for the gross (coarse) translation of the optical elements over the disk surface from one area of the disk to another. This has generally been accomplished by mounting the optics in a carriage actuator. Relatively widely spaced coarse servo tracks are then used to determine actuator and optical head position as the actuator moves across the disk surface. See e.g., U.S. Pat. No. 4,094,010, issued June 6, 1978, to Pepperl et al., teaching the placement of a plurality of concentric coarse seek tracks on a disk surface.
In addition to coarse seek movement over the disk surface, fine seek movement from track to track is necessary. For proper operation, the coarse seek and the fine seek tracking components must cooperate, not only in seeking a new location, but also in maintaining proper tracking once the proper track is attained. See U.S. Pat. No. 4,330,880, issued May 18, 1982, to Van Dijk.
For fine tracking of the focused beam over the disk surface, prior devices have taught the use of a pair of tracking spots focused on opposite edges of a track, and comparing the strength of the reflected signals. For example, see U.S. Pat. No. 4,243,850, issued Jan. 6, 1981, to Edwards; U.S. Pat. No. 4,305,081, issued Dec. 8, 1981, to Spong; and U.S. Pat. No. 4,059,841, issued Nov. 22, 1977, to Bricot et al.
In recent years, there has been increased interest in the development of optical storage devices which can record as well as read optical information. See e.g. U.S. Pat. No. 4,363,116, issued Dec. 7, 1982, to Kleuters et al., wherein a single laser is used to both record data on, and to read data from, the disk surface. However, there has also been increased interest in the use of multi-laser systems for both reading and writing. See U.S. Pat. No. 4,198,701, issued Apr. 15, 1980, to Reddersen et al., and U.S. Pat. No. 4,334,299, issued June 8, 1982, to Komurasaki et al,. When writing new data tracks on a disk surface, it is usually necessary to track on a previously written track because ordinarily it is quite difficult to maintain proper track spacing while writing on the present track. In multi-laser recording systems, it is more efficient to both combine the read and write beams so that they can share some part of the optical path and corresponding elements.
While earlier developments have embodied some of the basic concepts, they suffered from an inability to combine all these elements into a single working optical device for both recording and reading high density data. The present invention answers an unmet need for a specific implementation of all the diverse optical elements necessary to generate coarse seek tracking, fine tracking, focusing, and data reading means, all coupled to a means for writing new data on the disk.
The prior developments have not been able to systematically combine all of the disparate elements needed for a coarse seek read and write device into a single working set of optical elements. The known teachings have also been unable to provide a completely integrated means for combining a plurality of optical paths into a single path, thus simplifying the optics. The disclosed invention addresses this problem by disclosing a complete optical system for recording and reading optical media. This is accomplished by both improving upon the previously known concepts and by developing new concepts, which together provide an optical system that is able to generate and transmit to the recording surface, complete means for recording and reading optical data. The disclosed invention provides an integrated system, teaching the use of coarse seek, write and read optical trains (a train being the set of optical elements used to direct the beam along its optical path). More particularly, the disclosed invention teaches the efficient combination of all three beams so as to share some number of optical elements in common.
It is an object of the disclosed invention to provide an optical system for reading and writing data in an optical information storage system.
It is another object of the disclosed invention to provide a means for combining a coarse seek, read and write optical train into a single optical information storage device.
It is yet another object of the disclosed invention to provide a means for selectively combining and separating the coarse seek, read and write optical trains, so that the beams can share a number of optical elements in common.